Many aircraft employ moving map displays. On the military side, for example, they are used in the A-7D and A-7E as well as on the F-111D. They are also the subject of continuing development efforts in various military programs.
An optimal moving map display system for use in military aircraft would have the capability of providing a full color topographical map display with a high level of terrain detail under conditions of high brightness, contrast and resolution and in a system which satisfies current military constraints involving not only the usual environmental mil. specs. relating to shock, vibration, temperature, moisture, etc., but also the particularly stringent requirements of attack-type aircraft dealing with weight and cockpit space. Ideally, the display should be depictable on a multi-purpose cockpit display and have capabilities for radar superposition, real-time annotation, zoom/de-zoom, scaling, and selectable stabilization modes (e.g., "north-up", "track-up", or "heading-up"). To maximize operating life, to minimize mean time between failures and maintenance schedules, and to optimize reliability and ruggedness, the system should preferably have no or few moving parts.
An ideal system should also provide large area coverage (e.g., 450.times.450 nmr*) as well as accurate registration between the depicted terrain or other reference data and the vehicle indicator or other reference indicia. FNT *nautical miles
There are a wide variety of designs of moving map display systems. One type employs servo-driven film projector systems wherein the film position is mechanically positioned in accordance with vehicle position. These systems are capable of providing full color map renditions but are deficient in annotation capabilities and are burdened with the usual shortcomings associated with mechanical film translation and rotation schemes (e.g., weight and volume penalties, and less-than-optimum reliability and registration accuracy). As dedicated displays these systems also consume prime cockpit space.
Another technique involves the use of a computer generated map displayed on a CRT. This system is limited in the level of terrain detail that can be provided; only a schematic representation is displayed and it requires a dedicated computer to provide constant update of position and orientation.
Still another approach provides annotation capabilities in a combined optical/CRT system by means of a special rear-ported, CRT having one or more rear apertures or ports through which the optical terrain images and other data are projected; to annotate these presentations, the electron beam system of the CRT is appropriately deflected and modulated. Other combined displays optically combine CRT images with optical film projector images on a common screen, e.g., by using mirrors or prisms. In some of these combined systems holographic techniques are employed. These alternate methods generally have less-than-optimum brightness in the cockpit environment, consume substantial prime cockpit space and, to the extent they employ mechanical positioning, are burdened with the limitations previously described.
Some examples of the above-described display systems include the Horizontal Situation Display (HSD) system manufactured by Astronautics Corporation of America, the Projected Map System (PMS 4 & 5) manufactured by Computing Devices of Canada Ltd., and the AN/ASN 99 and Combined Display System (CDS-1) of the same company.